1. Field of the Invention
The present invention relates to a braking apparatus, and more particularly to a braking apparatus having a function of detecting brake actuation and release faults.
2. Description of the Related Art
A motor braking apparatus releases braking by applying a voltage. However, due to a fault such as a cable or brake coil break or a relay breakage, it may not be possible to release the brake even when a voltage is applied. On the other hand, if relay contacts are fused, the brake may remain released, which can lead to a situation in which an axis driven by the motor drops thus causing damage to a tool or a workpiece. To address this, brake fault detection methods have been developed (for example, refer to Japanese Unexamined Patent Publication Nos. 2014-50912 and 2014-10546, hereinafter referred to as “Patent Document 1” and “Patent Document 2”, respectively).
A brake drive control apparatus disclosed in Patent Document 1 comprises a voltage detection unit which detects a braking voltage applied to a brake, a switch command delaying unit which delays a switch command, and a short-circuit fault determining unit which, based on the delayed switch command, determines whether a short-circuit fault has occurred to a switching device.
A brake fault diagnostic apparatus disclosed in Patent Document 2 comprises a fault diagnostic unit which performs diagnosis to determine whether there is a brake fault or not when a motor is energized and the brake is in an actuated state, and an output unit which, when a brake fault is detected, outputs a brake fault signal without deenergizing the motor and without releasing the brake.
FIG. 1 is a diagram showing the configuration of a conventional art braking apparatus 1000. A voltage (for example, 24 [V]) supplied from a DC power supply 1002 is applied via a cable 1003, a switch 1004, a spark killer 1005, and a surge absorber 1006 to the terminals 1008 and 1009 of a brake 1007. The brake 1007 is provided with a brake coil 1001.
The structure of a brake used in a motor (hereinafter also called an “electrical motor”) will be described. FIG. 2 shows a cross-sectional view of a conventional art brake. A friction plate 1012 is attached to a motor shaft 1010 via a hub 1011. An end plate 1013 is provided on one face of the friction plate 1012, and an armature 1014 is provided on the other face. The end plate 1013 is fixed to a core 1017 with a bolt 1016 by interposing a spacer 1015 therebetween. The armature 1014 is mounted so as to be slidable along the longitudinal direction of the bolt 1016.
The core 1017 is provided with a brake coil 1001. When the voltage applied to the brake coil 1001 is 0 [V], the armature 1014 is pressed against the friction plate 1012 by a spring 1018a, as shown in the left part of FIG. 2. As a result, a first friction part 1019 is formed between the friction plate 1012 and the end plate 1013 and a second friction part 1020 is formed between the friction plate 1012 and the armature 1014. With this friction, the brake is actuated, and the motor is locked in a given position, thus putting the brake in a locked state.
On the other hand, when the voltage applied to the brake coil 1001 is a brake releasing voltage (for example, 24 [V]), a magnetic attraction force M greater than the pressing force of the spring 1018b is exerted due to a magnetic flux Φ, and the spring 1018b is compressed, thus disengaging the armature 1014 from the friction plate 1012. As a result, the first friction part 1019 formed between the friction plate 1012 and the end plate 1013 and the second friction part 1020 formed between the friction plate 1012 and the armature 1014 no longer exist. Consequently, the brake is released, thus putting the brake in a released state.
A possible cause for a fault that can occur in the braking apparatus may be a break in the brake coil 1001. Other possible causes include a break in the cable 1003 and a fusing of the switch 1004.
However, in the conventional art braking apparatus, it has not been easy to check the actual released state of the brake and to identify a cause for a brake release fault. More specifically, it has not been possible to check whether the brake has actually been released when a voltage is applied to the brake. As a result, if the motor is driven when the brake is not actually released, the brake may be dragged, resulting in damage to the brake friction parts or causing damage (such as an insulation failure or winding resistance failure) to the motor due to the frictional heat of the brake. On the other hand, when the voltage to the brake is turned off in order to apply the brake, if the brake remains released, the axis driven by the motor may drop thus causing damage to a tool or a workpiece.